Attitude sensing by amplitude comparison of multiple radar beams



y 18, 1965 c. J. BADEWITZ 3,184,736

ATTITUDE SENSING BY AMPLITUDE COMPARISON OF MULTIPLE RADAR BEAMS FiledNov. 28, 1962 2 Sheets-Sheet 1 VEHICLE x AXIS VERTICAL g BEAM l4 BEAM o-SURFAGE Fig. l

VEHICLE SPECULAR REFLECTIVITY REFLECTIVITY AVERAGE SLOPE t CURVE0.8db/DEGREE l6 db BEAM 10 o m DIFFUSE REFLECTIVITY E BEAM I2 36' '6 so0 3o ANGLE OF lNCiDENCE ANGLE OF INCIDENCE l A q- 3 Fig.2

INVENTOR. CHARLES J. BA DEWFI'Z BY W8W y 13, 1965 c. J. BADEWITZ3,184,736

ATTITUDE SENSING BY AMPLITUDE COMPARISON OF MULTIPLE RADAR BEAMS FiledNov. 28, 1962 2 Sheets-Sheet 2 LEFT MIxER l6 FRoNT 26 RADAR 543:; MIXERTRANSMITTER 28 22 Egg; MIXER Fig.4

+LEFT FRoNT AMPLITu0E LAA'ESRAL LATERAL CHANNEL coMPARAToR DETECTORCONTROL 32 34 3 42 I L R 30 RIGHT FROM 1 5o CHANNEL U D 40 44 /I\' 48 36I l RlGHT REAR AMPUTUDE +L0fgl'lglNAL LONGITUDINAL cHANNEL COMPARATORDETECTOR CONTROL ROTATING 52 MIXER RADAR ANTENNA TRANsMITTeR ROTATING 54I /MEcHANIsM i 56 AZIMUTH I sENsoR 46 r LEFT FRONT AMPLITUDE LIELESFALLATERAL CHANNEL COMPARATOR DETECTOR coNTRoL 32 34 3 42 I IVA-NR RIGHTFRONT so 50/ A D cHANNEL I 36 0 44 A 48 i RIGHT REAR AMPLITUDE Loggg uolNAL LONGITUDINAL CHANNEL 7 COMPARATOR DETECTOR coNTRoL INVENTOR.

cHARLEs J. BADEWITZ Fig. 5 BY United States Patent 3,184,736 ATTTUIBESENSING BY AMFLETUDE MPARE= SQN 6F RADAR BEAMS Charles .I. Badcwitz, SanDiego, (Ialih, assignor to The Ryan Aeronautical (10., San Diego, Caiif.Filed Nov. 28, 1962, Ser. No. 24%,609 7 Claims. (Cl. 343-) Thisinvention relates generally to radar navigation and altimeter systemsand particularly to a radar system for sensing vehicle attitude relativeto a reflecting surface.

BACKGROUND Various radar systems for determination of range, azimuth,speed, drift, and altitude are known to the art. Pulse, frequencymodulation, and Doppler techniques applied to such systems also are wellknown. Some systems use a plurality of fixed beams while others sweep asingle beam through known positions. In all radar systems,electromagnetic waves are reflected back to a radiation source by anobject, one or more characteristics of the waves being used to indicatea specific quantity. Simple pulse radar, for example, uses the constantvelocity of electromagnetic waves in space to measure range and adirectional antenna to indicate azimuth from the source to an object. Asystem for measuring the speed and drift of an airborne vehicle may usetwo or more fixed beams or a single beam swept through two or more knownpositions; differences in characteristics of the reflected signals, thenare used to compute ground speed and drift, the Doppler frequency shiftbeing a frequently used characteristic.

The instant invention senses airborne vehicle attitude relative to areflecting surface by comparing the amplitudes of three or morereflected signals originated by fixed beams or a single beam sweptthrough three or more fixed positions.

This invention may be used as a single system or, more economically, bysupplementary modification of an existing system that performs otherfunctions.

OBJECTS It is a principal object of this invention to provide a simplevehicle attitude sensing system that is readily adaptable to an existingsystem using a plurality of electromagnetic beams to perform otherfunctions.

It is another object of this invention to provide an improved system formore effective detection of terrain irregularities.

The attitude sensing function may be used with other systems in mannedor unmanned vehicles for detection of terrain dissimilarity,determination of whether the reflecting surface is level or not, checkand calibration of other systems, and control of vehicle maneuvers.

With these and other objects definitely in View, this invention consistsin the novel combination and arrangement of elements as will behereinafter fully described in the specification, particularly pointedout in the claims, and illustrated in the drawings that form a materialpart of this disclosure, and of which:

FIGURE 1 shows the vehicle beam relationship.

FIGURE 2 is a reflectivity curve plotted against beam angle ofincidence.

FIGURE 3 compares the reflectivity of two beams at different angles ofincidence.

FIGURE 4 is a block diagram of an embodiment using three fixed beams.

FIGURE 5 is a block diagram of an embodiment using a single swept beam.

DETAILED DESCRIPTION In FIGURE 1, three fixed beams are shown directedin a downward direction in different quadrants at the same anglerelative to the longitudinal and transverse axes of a vehicle. Two beamsit) and 12 are oriented forward and to the left and right of thevehicles longitudinal axis. A third beam 14 is oriented rearward and tothe right of the longitudinal axis of the vehicle. The same presentationalso could be used to illustrate three momentary positions of a single,swept beam.

When the reflecting surface and the vehicles flight attitude are level,the angles of incidence of the three beams are equal, the lengths of thethree beams are equal, and the amplitudes of the three reflected beamsare equal, assuming reflectivity of the reflecting surface is uniform.Under these conditions, deviations from level flight change the anglesof incidence, lengths, and relative amplitudes of the beams, reflectedbeams it and 12 indicating transverse angular errors relative to thevehicles longitudinal axis and reflected beams 12 and 14 indicatinglongitudinal angular errors relative to the vehicles transverse axis. Inconventional aircraft, a difference in amplitude between beams iii and12 indicates the wings are not level requiring right or left controlstick aileron correction; and a difference in amplitude between beams 12and 1 5 indicates the fuselage is not level, requiring up or downcontrol stick elevator correction.

FIGURE 2 shows the reflectivity of a uniform reflecting surface,indicating maximum reflectivity at zero angle of incidence, droppingsharply to an inappreciable magnitude at degrees and above. Inaccordance with this reflectivity characteristic, a reflected beamrotating toward the vertical increases in amplitude, while a reflectedbeam rotating away from the vertical decreases in amplitude.

In FIGURE 3, a vehicle is shown in a flight attitude 10 degrees from thevertical or level flight. In conventional aircraft, the left wing wouldbe down with beam Ill rotated transversely about the longitudinal axistoward the vertical, and the right wing would be up with beam 12 rotatedtransversely about the longitudinal axis away from the vertical. The twobeams plotted against a reflectivity response curve indicate a 16 dbdifference in amplitude.

Since a 3 db change is detectable by the average human ear and changesof lower magnitude are detectable by sensitive instruments, the methodof the instant invention provides a sensitive detector of vehicleattitude changes. Changes in terrain contours and surface reflectivityalso are readily detected.

In one embodiment of this invention, as illustrated in FIGURE 4, fixedantenna beams are employed. Radar transmitter 1t; couples energy throughmixers 18, 2t and 22 to fixed, directional antennas 24, 26 and 28.Antennas 24 and 26 radiate sharply defined beams forward and downward,one to the left and the other to the right of the vehicles longitudinalaxis. Antenna 28 performs a similar function rearward, downward, and tothe right. Antenna 28 could be directed to the left with no change insystem performance. The coupled energy from transmitter 15 may have anycharacteristic known to the art, and antennas 24, 2s and 28 may beenergized simultaneously or sequentially. Reflected energy is receivedby antennas 24, 26 and 2t; and coupled by mixers 18, 2d and 22 to radarreceiver 36'. Signals from the three antennas are kept separated inreceiver channels 32, 34 and 36 and compared in amplitude comparators 3Sand 4%). Amplitude comparator 38 compares signals from the two forwardantennas, while amplitude comparator 40 compares signals from the rightforward and. rearward antennas. When the signal amplitudes are equal,amplitude comparators 38 and 40 have no output.

When the amplitudes of signals fed to amplitude comparator 38 areunequal, the difference signal is fed to lateral error detector 42.Similarly, a difference signal 3,1 saves output of amplitude comparator40 is fed to longitudinal error detector 44. In either case, the errorsignal is either positive or negative. If the error signal is used tocontrol flight attitude, the lateral error signal is fed to lateral orsimilar control 46 and the longitudinal error signal is fed tolongitudinal or similar control 48. In both cases, the effect of theerror signal restores the vehicle to level flight. The error signals mayalso be fed to error indicator 50 in which transverse errors are shownto left or right indicating the left or right forward beam amplitude isgreater, and longitudinal errors are shown up or down indicating theright forward or rearward beam amplitude is geater. These indications,by comparison with the indications of other systems, may be used toindicate terrain that is uneven in contour or reflectivity or areflecting surface that is not level.

A second embodiment, shown in FIGURE 5, uses a rotating antenna to sweepa beam continuously through 360 degrees at a downward anglecorresponding to that of the fixed beams in the first embodiment. Radartransmitter 16 energizes rotating, directional antenna 52 through mixer54. Antenna 52, thus, radiates energy through 360 degrees.Alternatively, radar transmitter 16 could be timed to energize antenna52 only when the antenna is oriented momentarily at selected azimuthpoints.

Reflected energy is received by antenna 52 through 360 degrees or,alternatively, at said selected azimuth points and coupled by mixer 54to azimuth sensor 56. An additional signal from antenna rotatingmechanism 58 to azimuth sensor 56 enables azimuth sensor 56 to rejectall reflected energy except at azimuths corresponding to positions ofthe fixed beams in the first embodiment. As a result, reflected signalsare fed by azimuth sensor 5'6 to radar receiver 30 with essentially thesame characteristics as the signals of the fixed beams in the firstembodiment. The signals are kept separated in channels .32, 34 and 36and utilized in the same manner as in the first embodiment.

In conjunction with sensing vehicle attitude and terraininconsistencies, this system may be used to provide vertical correctionsignals to other systems, such as gyros, artificial horizons, andinertial systems that are subject to drift or change from one referenceobject or system to another.

It is understood that minor variation from the form of the inventiondisclosed herein maybe made without departure from the spirit and scopeof the invention, and that the specification and drawing are to beconsidered as merely illustrative rather than limiting.

' I claim:

1. A method of sensing vehicle attitude relative to terrain comprisingthe steps of:

radiating electromagnetic beams in at least three different fixeddownward directions relative to the normal attitude of the vehicle;

receiving each beam reflected along the same path as radiated;

comparing the amplitudes of the separate beams; and

deriving from the comparative amplitudes the attitude of the vehiclerelative to the terrain surface reflecting the beams.

2. The method of claim 1 in which at least two of said directions areforward to the left and right of the longitudinal axis of said vehicle,and at least one of said directions is rearward in the samelongitudinal, inclined plane as one of the forward directions.

3. In a radar system for a vehicle including a transmitter and areceiver, thecombination comprising:

antenna means radiating signals in at least three different, fixeddownward directions relative to the normal attitude of the vehicle, eachradiated signal being reflected and received along the same path asradiated;

means for sensing amplitude equality and difference between thereflected signals; and means for deriving from the comparativeamplitudes the attitude of the vehicle relative to vertical.

4. In a radar system for a vehicle including a transmitter and areceiver, the combination comprising:

antenna means radiating signals in at least two fixed downward, forwarddirections to the left and right of the longitudinal axis of saidvehicle, and at least one fixed downward, rearward direction in the samelongitudinal inclined plane as one or" the forward directed antennameans, said directions being relative to the normal attitude of saidvehicle;

and amplitude comparator means for converting diiference in amplitudesof the forward directed reflected signals into transverse attitude errorsignals and converting difi erence in amplitudes of the forward andrearward directed signals in the same longitudinal inclined plane intolongitudinal attitude error signals.

5. Apparatus according to claim 4 in which said antenna means includesdirectional antennas which are fixed relative to the vehicle.

6. Apparatus according to claim 4 in which said antenna means includes arotating, directional antenna and means for rejecting all reflectedsignals except those reflected from said directions. a

7. Apparatus according to claim 4 and including means for correctingvehicle attitude with said error signals.

References Cited by the Examiner UNITED STATES PATENTS 2,412,003 12/46Neufeld 343-? 2,499,349 3/50 Ayres 343-7 2,965,894 12/60 Sweeney 343-.72,987,026 6/61 Cunningham 343,7 3,028,592 4/62 Parr et al. 343-73,090,583 5/63 Behun et al 343100 3,095,562 6/63 Dworetzky et al. 343-83,102,263 8/63 Meyer 343-8 CHESTER L. JUSTUS, Primary Examiner.

1. A METHOD OF SENSING VEHICLE ATITUDE RELATIVE TO TERRAIN COMPRISINGTHE STEPS OF: RADIATING ELECTROMAGNETIC BEAMS IN AT LEAST THREEDIFFERENT FIXED DOWNWARD DIRECTIONS RELATIVE TO THE NORMAL ATITUDE OFTHE VEHICLE; RECEIVING EACH BEAM REFLECTED ALONG THE SAME PATH ASRADIATED; COMPARING THE AMLITUDES OF THE SEPARATE BEAMS; AND DERIVINGFROM THE COMPARATIVE AMPLITUDES THE ATTITUDE OF THE VEHICLE RELATIVE TOTHE TERRAIN SURFACE REFLECTING THE BEAMS.
 3. IN A RADAR SYSTEM FOR AVEHICLE INCLUDING A TRANSMITTER AND A RECEIVER, THE COMBINATIONCOMPRISING: ANTENNA MEANS RADIATING SIGNALS IN AT LEAST THREE DIFFERENT,FIXED DOWNWARD DIRECTIONS RELATIVE TO THE NORMAL ATTITUDE OF THEVEHICLE, EACH RADIATED SIGNAL BEING REFLECTED AND RECEIVED ALONG THESAME PATH AS RADIATED; MEANS FOR SENSING EQUALITY AND DIFFERENCE BETWEENTHE REFLECTED SIGNALS; AND MEANS FOR DERIVING FROM THE COMPARATIVEAMPLITUDES THE ATTITUDE OF THE VEHICLE RELATIVE TO VERTICAL.